The use of lasers to erode all or a portion of a workpiece's surface is known in the art. In the field of ophthalmic medicine, modification of corneal curvature is known to be accomplished using ultraviolet or infrared lasers. The procedure has been referred to as “corneal sculpting.”
In such a procedure, application of the treatment laser during unwanted eye movement can degrade the refractive outcome of the surgery. The eye movement or eye positioning is critical since the treatment laser is centered on the patient's theoretical visual axis which, practically speaking, is approximately the center of the patient's pupil. However, this visual axis is difficult to determine due in part to residual eye movement and involuntary eye movement known as saccadic eye movement.
Video-based eye tracking systems automatically recognize and track the position of the eye based upon landmarks present within an image of a human eye. Video-based systems, however, have neither sufficient speed nor accuracy to detect high-speed movement.
Previous disclosure of eye tracking systems and methods has been made in U.S. Pat. Nos. 5,980,513; 6,315,773; and 6,451,008, which are co-owned with the present application, and which are hereby incorporated by reference hereinto. In these patents, an eye treatment laser beam delivery and eye tracking system is provided (FIG. 1). A treatment laser and its projection optics generate laser light along an original beam path (i.e., the optical axis of the system) at an energy level suitable for treating the eye. An optical translator shifts the original beam path in accordance with a specific scanning pattern so that the original beam is shifted onto a resulting beam path that is parallel to the original beam path. An optical angle adjuster changes the resulting beam path's angle relative to the original beam path such that the laser light is incident on the eye.
An eye movement sensor detects measurable amounts of movement of the eye relative to the system's optical axis and then generates error control signals indicative of the movement. The parallel relationship between the eye movement sensor's delivery light path and the treatment laser's resulting beam path is maintained by the optical angle adjuster. In this way, the treatment laser light and the eye movement sensor's light energy are incident on the eye in their parallel relationship.
A portion of the eye movement sensor's light energy is reflected from the eye as reflected energy traveling on a reflected light path back through the optical angle adjuster. The optical receiving arrangement detects the reflected energy and generates the error control signals based on the reflected energy. The optical angle adjuster is responsive to the error control signals to change the treatment laser's resulting beam path and the eye movement sensor's delivery light path in correspondence with one another. In this way, the beam originating from the treatment laser and the light energy originating from the eye movement sensor track along with the eye's movement.
The laser beam delivery and eye tracking system 10 includes treatment laser source 11, projection optics 12, X-Y translation mirror optics 13, beam translation controller 14, dichroic beamsplitter 15, and beam angle adjustment mirror optics 16.
After exiting the projection optics 12, beam 17 impinges on X-Y translation mirror optics 13, where beam 17 is translated or shifted independently along each of two orthogonal translation axes as governed by beam translation controller 14.
The eye tracking portion of system 10 includes eye movement sensor 18, dichroic beamsplitter 15, and beam angle adjustment mirror optics 16. The sensor 18 determines the amount of eye movement and uses same to adjust mirrors 19 and 20 to track along with such eye movement. To do this, sensor 18 first transmits light energy 21, which has been selected to transmit through dichroic beamsplitter 15. At the same time, after undergoing beam translation in accordance with the particular treatment procedure, beam 17 impinges on dichroic beamsplitter 15, which has been selected to reflect beam 17 to the beam angle adjustment mirror optics 16.
Light energy 21 and beam 17 preferably retain their parallel relationship when they are incident on an eye 23. Beam angle adjustment mirror optics 16 consists of independently rotating mirrors 19 and 20 under servo control.
Light energy reflected from the eye 23 travels back through optics 16 and beamsplitter 15 for detection at sensor 18. Sensor 18 determines the amount of eye movement based on the changes in reflection energy 22. Error control signals indicative of the amount of eye movement are fed back by sensor 18 to beam angle adjustment mirror optics 16. The error control signals govern the movement or realignment of mirrors 19 and 20 in an effort to drive the error control signals to zero. In doing this, light energy 21 and beam 17 are moved in correspondence with eye movement while the actual position of beam 17 relative to the center of the pupil is controlled by X-Y translation mirror optics 13.
The light energy should preferably lie outside the visible spectrum so as not to interfere or obstruct a surgeon's view of eye 23, and must be “eye safe” as defined by the American National Standards Institute (ANSI), for example, light energy 21 may be infrared light energy in the 900-nanometer wavelength region.
Sensor 18 may be broken down into a delivery portion and a receiving portion (FIG. 2). Essentially, the delivery portion projects light energy 21 in the form of light spots 24–27 onto a boundary (e.g., iris/pupil boundary 28) on the surface of eye 23. The receiving portion monitors light energy 22 in the form of reflections caused by light spots 24–27.
In use, spots 24 and 26 are focused and positioned on axis 29, while spots 25 and 27 are focused and positioned on axis 30 as shown. Axes 29,30 are orthogonal to one another. Spots 24–27 are focused to be incident on and evenly spaced about iris/pupil boundary 28. The four spots 24–27 are of substantially equal energy and are spaced substantially evenly about and on iris/pupil boundary 28. This placement provides for two-axis motion sensing as described in the above-referenced co-owned patents.
This tracking system 10 is effective for eyes dilated to greater than approximately 5.5 mm. It would be desirable to be able to track undilated eyes and those that, even dilated, are less than 5.5 mm, or that have an irregular shape.